The present invention relates generally to a flexible duct or hose assembly utilized for transferring pressurized air or other gases or even fluids in aerospace and commercial applications. In particular, the present invention is directed to flexible hose assembly having greatly improved bonding strength and resulting stiffness, significant cost and weight savings while, at the same time, demonstrating better performance due to higher strength and pressure capability as compared to conventional flexible hose assemblies. The improved hose assembly has a wider and higher range of operating temperatures and pressures with enhanced protection against leaks and burns.
Currently, conventional ducts or hoses consist of some variation of the standard three-part assembly. A round helix is bonded to the external or internal surface of an internal liner and the helix is, itself, surrounded by an external reinforcing cord. This assembly allows the hose to sustain pressure loads while providing the flexibility needed to compensate for misalignment between component members. The external, protective cord is designed to prevent movement of the helix, which would otherwise result in delamination of the internal liner. In such a hose assembly, the external reinforcing cord may be formed of fiberglass, nylon, polyester or even cotton. The internal liner may be formed of silicone, neoprene, nitriles, vinyls, fluorosilicones, butyls or any well known rubber product. Finally, the helix is usually formed of spring steel wire or nylon (polyamide).
When forming a conventional, round helix or steel wire or nylon, costly processing steps, coatings and chemical treatments are necessary to achieve a satisfactory bond with the internal liner. Because of the difficulty in achieving such a bond, the external fiberglass cord often must be applied on both sides of the helix to prevent air pockets from being developed between the helix and the liner. The external cord is also necessary to prevent the helix from floating within the hose assembly due to inadequate bonding as well as to apply pressure during curing process. If the outer cord is not properly applied, the helix still may be free to move, resulting in delamination of the internal liner and ultimate failure of the hose assembly. Such failure may result in ballooning, rupture or internal blockage of the gas or fluid being transmitted through the hose assembly. The outer cord adds significant weight to the hose as well as increasing the overall cost of manufacturing the hose. A further drawback of conventional flexible hose assemblies resides in the use of nylon to form the helix. While nylon cannot be employed in applications in excess of 200 degrees F, it is currently acceptable for use in limited high temperature applications.
Conventional aircraft hoses extend between and are attached to component structures, i.e., pressure tanks, wall ports, hose outlets, by sliding the flexible ends of the hose's internal liner over beaded, protruding, round, oval, or similarly shaped extensions formed on the component structures. A band clamp, similar to those employed on automobile hoses, is manually positioned to surround both the beaded end of the component and overlapping portion of the liner before being tightened. Alternatively, when joining the beaded ends of two separate components to form a continuous hose assembly, a flexible sleeve is usually employed to overlap the beaded end portions. A separate band clamp is disposed to encircle each of the beaded end portions as well as the overlapping end portions of the sleeve. Each of the band clamps is systematically tightened, usually by turning a screw, to form a leak proof passageway between the sleeve and the components.
Conventional band clamps must be periodically inspected and adjusted to assure that the fluid tight connection is maintained between the hose and component or between two hoses connected by an overlapping sleeve. Such inspection and maintenance is expensive and labor intensive in the need for periodically retightening and repositioning the band clamps. The metallic band clamps are heavy and not very reliable. Overtightening or improper alignment of a band clamp can cause damage to the component joined to the hose and/or possible tearing of the flexible sleeve when employed in hose-to-hose connections. Destruction of the component or sleeve by over-torquing can lead to pressure loss throughout the flexible hose assembly. This, in turn, can readily lead to component failure and passenger discomfort, if the hose at high altitude for delivering oxygen to within an aircraft. Frequently, sleeves extending between and overlapping the end portions of the separate hoses will leak around one or both of the band clamps due to mating surface irregularity/deformation. The standard response to any resulting air and fluid leaks is additional tightening of the clamp which can easily lead to over-torquing the band clamp. Alternatively the relatively expensive process of employing fillers, reinforcements or weldments is employed to reduce leaks between the hose and component.
In an effort to overcome the problems associated with conventional metallic band clamps, U.S. Pat. No. 5,622,394 suggests that a metal ferrule be permanently, mechanically crimped onto the hose. There is no ability to alter the engagement pressure between the ferrule and the hose and if excessive pressure is applied to the ferrule, the result will be the same as over-torquing a clamp band. Additionally, replacing a damaged duct will normally require expensive removal application methods and tools for removing the crimped ferrule. In many areas the crimped ferrule is impossible to remove due to its inaccessibility.
Another proposed solution to the band clamp problem is shown in U.S. Pat. No. 5,388,870 wherein differences in the biconical shapes of the mating members provides a clamping force for maintaining the hose in place. Such an assembly could not be employed with standard beaded conduit members as routinely found in the aerospace field.
A yet further attempt to overcome the problems associated with conventional band clamps is found in the assembly taught in U.S. Pat. No. 5,340,167 which employs a heat shrinkable tubing clamp. This assembly cannot be easily mounted by hand and, more importantly, there is no self-adjustment capability once the clamp is deployed into its final location. This system is not applicable to the aircraft and automobile industries because it doe not meet FM regulations for burn resistance requirements and exposure to heat will continue to shrink and break. This system also does not sustain pressure loading.
Based on the above and foregoing, it can readily be appreciated that there presently exits a need in the art for a flexible hose assembly which overcomes the weight, cost and production problems associated with known flexible hose assemblies. There also exists a need for overcoming the bonding problems between the helix and the internal liner as well as a need for constructing a flexible hose assembly capable of operating at high temperatures and pressures. Finally, there is a need for a band clamp which can be easily applied, preferably self-adjustable, automatically provides additional clamp-up with increased pressure and is not capable of over-torquing.
As will become apparent hereinafter, the present invention fulfills these needs by providing a hose assembly employing a uniquely formed helix capable of increased bonding with the internal liner which eliminates the need for any separate reinforcement cord. The materials utilized in constructing the helix are carefully chosen to assure operation at a wide range of temperatures and pressures. A retainer ring constructed in accordance with the present invention can be easily positioned about the hose and component or sleeve by merely sliding the retainer ring. Once in position, the retainer ring engages the beaded end portion of the component to form a self-adjusting fluid tight connection that automatically increases in strength as the load on the hose increases. This creates a positive seal that is leak-proof and capable of withstanding variations in pressure and temperature without need for any additional application of torque by the operator as required with conventional band clamp assemblies.